This invention relates to an air conditioner and, more particularly, to an improvement in an air conditioner having a compressor motor which is driven at a variable speed by an inverting apparatus.
Recently, air conditioners in which the rotating speed of a compressor motor is driven at a variable speed by an inverting apparatus are rapidly coming into widespread use, since they are excellent in terms of energy saving and comfort as compared with conventional air conditioners in which the compressor motor is ON/OFF controlled.
However, hitherto, there is only one kind of an output voltage to frequency ratio pattern (hereinafter, referred to as a V/f pattern) of the inverting apparatus for driving the compressor motor of the air conditioner at a variable speed. The compressor motor is driven at a constant V/f ratio irrespective of the load condition of the air conditioner, so that there is a drawback such that it is difficult to perform the operation with high efficiency. In addition, there is another drawback such that the operation of the compressor motor becomes unstable depending upon a variation in load.
Therefore, the technology such that a V/f value of the inverting apparatus is varied by detecting the current of the motor which is driven at a variable speed, is disclosed in the Official Gazette of Japanese Patent application Laid-Open No. 183297/1982.
However, in this case, since the variation in the motor current is large even in the stable state, the motor current, is not the optimum subject for detection of the variation of the load condition and there is a risk of erroneous detection. Consequently, it is not always best to apply such technology to the inverting apparatus of the air conditioner. In other words, the V/f value of the inverting apparatus cannot be always set to the optimum value in dependence on the load variation of the air conditioner, so that the compressor motor cannot always be stably operated with high efficiency.